MDEV-22758 Assertion `!item->null_value' failed in Type_handler_inet6::make_sort_key_part

When some expression of an INET6 data type involves conversion to INET6 from
other data types, e.g. in:

- CAST:

    SELECT CAST(non_inet6_expr AS INET6)

- CASE and hybrid functions:

    SELECT CASE WHEN expr THEN inet6_expr ELSE non_inet6_expr END

- UNION:

    SELECT inet6_expr UNION SELECT non_inet6_expr

the result column must be fixed as NULL-able even if the non-inet6 expression itself
is not NULL-able, because at the execution time the conversion can fail.

Details:
- Forcing NULL-ability if conversion from some data type to INET6 is involved
  (for non-constant or for expensive expressions).
- Non-expensive constant expressions are tested for NULL-ability at fix_fields() time,
  so things like `CAST('::' AS INET6)` are still detected as NOT NULL.
- Adding "bool warn" parameter into a few methods, to avoid redundant warnings
  at fix_fields() time when calculating NULL-ability of constant values.

plugin/type_inet/mysql-test/type_inet/type_inet6.result

@@ -2058,3 +2058,54 @@ Lady of the Flies	::5
 Lord of the Ladybirds	::5
 Lord of the Ladybirds	::5
 DROP TABLE t1;
+#
+# MDEV-22758 Assertion `!item->null_value' failed in Type_handler_inet6::make_sort_key_part
+#
+CREATE TABLE t1 (a VARCHAR(8) NOT NULL, b INET6 NOT NULL);
+INSERT INTO t1 VALUES ('foo','::'),('bar','1::1');
+SELECT * FROM t1 ORDER BY CASE WHEN a THEN b ELSE a END;
+a	b
+foo	::
+bar	1::1
+Warnings:
+Warning	1292	Truncated incorrect DOUBLE value: 'foo'
+Warning	1292	Incorrect inet6 value: 'foo'
+Warning	1292	Truncated incorrect DOUBLE value: 'bar'
+Warning	1292	Incorrect inet6 value: 'bar'
+DROP TABLE t1;
+CREATE OR REPLACE TABLE t1 (a VARCHAR(8) NOT NULL);
+INSERT INTO t1 VALUES ('foo'),('bar');
+SELECT * FROM t1 ORDER BY CAST(a AS INET6);
+a
+foo
+bar
+Warnings:
+Warning	1292	Incorrect inet6 value: 'foo'
+Warning	1292	Incorrect inet6 value: 'bar'
+DROP TABLE t1;
+CREATE TABLE t1 (a INET6 NOT NULL, b VARCHAR(32) NOT NULL);
+CREATE TABLE t2 AS SELECT CAST(a AS INET6) AS ca, CAST(b AS INET6) AS cb FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `ca` inet6 NOT NULL,
+  `cb` inet6 DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+CREATE TABLE t2 AS SELECT COALESCE(a,a), COALESCE(a,b) FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `COALESCE(a,a)` inet6 NOT NULL,
+  `COALESCE(a,b)` inet6 DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+CREATE TABLE t2 AS SELECT a AS ca,a AS cb FROM t1 UNION SELECT a,b FROM t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `ca` inet6 NOT NULL DEFAULT '::',
+  `cb` inet6 DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t2;
+DROP TABLE t1;

plugin/type_inet/mysql-test/type_inet/type_inet6.test

@@ -1516,3 +1516,33 @@ SELECT name, PERCENTILE_DISC(1)
   WITHIN GROUP (ORDER BY star_rating)
   OVER (PARTITION BY name) AS pc FROM t1;
 DROP TABLE t1;
+
+
+--echo #
+--echo # MDEV-22758 Assertion `!item->null_value' failed in Type_handler_inet6::make_sort_key_part
+--echo #
+
+CREATE TABLE t1 (a VARCHAR(8) NOT NULL, b INET6 NOT NULL);
+INSERT INTO t1 VALUES ('foo','::'),('bar','1::1');
+SELECT * FROM t1 ORDER BY CASE WHEN a THEN b ELSE a END;
+DROP TABLE t1;
+
+CREATE OR REPLACE TABLE t1 (a VARCHAR(8) NOT NULL);
+INSERT INTO t1 VALUES ('foo'),('bar');
+SELECT * FROM t1 ORDER BY CAST(a AS INET6);
+DROP TABLE t1;
+
+CREATE TABLE t1 (a INET6 NOT NULL, b VARCHAR(32) NOT NULL);
+CREATE TABLE t2 AS SELECT CAST(a AS INET6) AS ca, CAST(b AS INET6) AS cb FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+
+CREATE TABLE t2 AS SELECT COALESCE(a,a), COALESCE(a,b) FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+
+CREATE TABLE t2 AS SELECT a AS ca,a AS cb FROM t1 UNION SELECT a,b FROM t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+
+DROP TABLE t1;

plugin/type_inet/sql_type_inet.cc

@@ -508,7 +508,19 @@ size_t Inet6::to_string(char *dst, size_t dstsize) const
 }
 
 
-bool Inet6::make_from_item(Item *item)
+bool Inet6::fix_fields_maybe_null_on_conversion_to_inet6(Item *item)
+{
+  if (item->maybe_null)
+    return true;
+  if (item->type_handler() == &type_handler_inet6)
+    return false;
+  if (!item->const_item() || item->is_expensive())
+    return true;
+  return Inet6_null(item, false).is_null();
+}
+
+
+bool Inet6::make_from_item(Item *item, bool warn)
 {
   if (item->type_handler() == &type_handler_inet6)
   {
@@ -523,18 +535,18 @@ bool Inet6::make_from_item(Item *item)
   }
   StringBufferInet6 tmp;
   String *str= item->val_str(&tmp);
-  return str ? make_from_character_or_binary_string(str) : true;
+  return str ? make_from_character_or_binary_string(str, warn) : true;
 }
 
 
-bool Inet6::make_from_character_or_binary_string(const String *str)
+bool Inet6::make_from_character_or_binary_string(const String *str, bool warn)
 {
   static Name name= type_handler_inet6.name();
   if (str->charset() != &my_charset_bin)
   {
     bool rc= character_string_to_ipv6(str->ptr(), str->length(),
                                       str->charset());
-    if (rc)
+    if (rc && warn)
       current_thd->push_warning_wrong_value(Sql_condition::WARN_LEVEL_WARN,
                                             name.ptr(),
                                             ErrConvString(str).ptr());
@@ -542,9 +554,10 @@ bool Inet6::make_from_character_or_binary_string(const String *str)
   }
   if (str->length() != sizeof(m_buffer))
   {
-    current_thd->push_warning_wrong_value(Sql_condition::WARN_LEVEL_WARN,
-                                          name.ptr(),
-                                          ErrConvString(str).ptr());
+    if (warn)
+      current_thd->push_warning_wrong_value(Sql_condition::WARN_LEVEL_WARN,
+                                            name.ptr(),
+                                            ErrConvString(str).ptr());
     return true;
   }
   DBUG_ASSERT(str->ptr() != m_buffer);
@@ -1036,6 +1049,8 @@ class Item_typecast_inet6: public Item_func
   bool fix_length_and_dec() override
   {
     Type_std_attributes::operator=(Type_std_attributes_inet6());
+    if (Inet6::fix_fields_maybe_null_on_conversion_to_inet6(args[0]))
+      maybe_null= true;
     return false;
   }
   String *val_str(String *to) override

plugin/type_inet/sql_type_inet.h

@@ -137,7 +137,7 @@ class Inet6
 {
 protected:
   char m_buffer[IN6_ADDR_SIZE];
-  bool make_from_item(Item *item);
+  bool make_from_item(Item *item, bool warn);
   bool ascii_to_ipv6(const char *str, size_t str_length);
   bool character_string_to_ipv6(const char *str, size_t str_length,
                                 CHARSET_INFO *cs)
@@ -152,7 +152,7 @@ class Inet6
     }
     return ascii_to_ipv6(str, str_length);
   }
-  bool make_from_character_or_binary_string(const String *str);
+  bool make_from_character_or_binary_string(const String *str, bool warn);
   bool binary_to_ipv6(const char *str, size_t length)
   {
     if (length != sizeof(m_buffer))
@@ -182,11 +182,17 @@ class Inet6
     return true;
   }
 
+  /*
+    Check at Item's fix_fields() time if "item" can return a nullable value
+    on conversion to INET6, or conversion produces a NOT NULL INET6 value.
+  */
+  static bool fix_fields_maybe_null_on_conversion_to_inet6(Item *item);
+
 public:
 
-  Inet6(Item *item, bool *error)
+  Inet6(Item *item, bool *error, bool warn= true)
   {
-    *error= make_from_item(item);
+    *error= make_from_item(item, warn);
   }
   void to_binary(char *str, size_t str_size) const
   {
@@ -264,8 +270,8 @@ class Inet6_null: public Inet6, public Null_flag
    :Inet6_null(str.ptr(), str.length())
   { }
   // Initialize from an Item
-  Inet6_null(Item *item)
-   :Null_flag(make_from_item(item))
+  Inet6_null(Item *item, bool warn= true)
+   :Null_flag(make_from_item(item, warn))
   { }
 public:
   const Inet6& to_inet6() const
@@ -714,6 +720,14 @@ class Type_handler_inet6: public Type_handler
   {
     attr->Type_std_attributes::operator=(Type_std_attributes_inet6());
     h->set_handler(this);
+    for (uint i= 0; i < nitems; i++)
+    {
+      if (Inet6::fix_fields_maybe_null_on_conversion_to_inet6(items[i]))
+      {
+        attr->set_maybe_null(true);
+        break;
+      }
+    }
     return false;
   }
   bool Item_func_min_max_fix_attributes(THD *thd,